Skinny Arcade or Fat Jet?

Science Nugget: Dec 04, 1998

The images above show the sudden appearance of a large structure in
the north polar crown region. A contour overlay shows the location of the
H-alpha filament and limb. The soft X-ray morphology calls to mind one
of the original soft X-ray jets discovered by Yohkoh SXT (Strong
et al., 1992), except that the 1991 jet was appropriately slender, whereas
this one is fat. We checked the BBSO image archive for this time, and found
that the appearance of the "fat jet" corresponded to the partial disappearance
of a filament. The images above show (as contours) the filament configurations
on Dec. 3 (day before) and Dec. 4 (just after) via Big Bear H-alpha. The
phenomenon might thus be interpreted as a skinny arcade rather than a fat
jet.

In any case, the appearance of the fat or skinny new structure followed
more typical microflare and jet activity near its southern footpoint. Although
a triggering relationship is always an extremely difficult matter to prove
rigorously, we can speculate here that the microflare/jet activity triggered
the large-scale event. However it is not very near the filament that erupted
could in any way have communicated physically with the region showing microflare
activity, so that the trigger action could have been independent of contact
(ie, without direct magnetic-field reconnection).

Note the twisted appearance of the "after" image - that's not supposed
to be there if helicity causes instability!

Suggestions welcome... a look at the EIT data would be worth the effort.